The problem of color removal from pulp and paper mill waste has been a subject of great consideration and investigation in the last few decades. An estimated two trillion gallons of wastewaters are discharged annually by the pulp and paper industry in major paper-producing countries and much of this effluent is highly colored. (Joyce et al., 1983).
The brownish color of the wastewater is mainly organic in nature primarily attributable to lignin degradation products formed during various pulping and bleaching operations (Srivastava et al., 1984, Dilek et al., 2000). The other color-imparting agents are wood-extractives, tannins, resins and synthetic dyes.
Color was never thought to be a major problem, being classified as a non-conventional pollutant. Some reasons for regulating color of waste water to protect fisheries or for aesthetic reasons. Additionally, the discharge of colored pulping effluents to the receiving waters has shown to inhibit photosynthetic activity of aquatic biota by reducing the penetration of sunlight and also have a direct toxic effects on biota.
The color compounds also chelate metal ions and may impart contamination due to heavy metals. Color causing organic compounds have also been implicated in the appearance of blue-green algal blooms (Paerl, 1982; Kuenzler et al., 1982; Witherspoon & Pierce, 1982). It is therefore, imperative that the color present in pulp and paper mill effluents be removed, before being discharged into receiving waters.
There are two general strategies for the removal of color from the effluent of a pulp & paper mill:
1) Conventional end of pipe treatment
2) Modification of the pulp and paper manufacturing process so that less color is produced.
The following technologies are conventionally used for removing color:
Secondary treatment in which the effluents are treated with conventional activated sludge method. However, conventional biological treatment systems cannot remove color (Yosefian et al., 2000).                Enzyme pre-treatment        Resin separation and ion exchange        Aluminum oxide        Adsorption on wood        Membrane processes        Irradiation        Electrolytic process        Activated carbon        Land treatment        Ozone        
At this point, no single technology has been identified as being the most effective for color removal. Since all the above-cited technologies are cost-intensive, they would have adverse economic impact on the mill involved. Moreover, chemical treatment processes add up to the ever-increasing concentration of chemicals in the environment (Kapdam et al., 2000).
In principle, decolorization is achievable using one or a combination of the following methods;
Adsorption
Filtration
Precipitation
Chemical degradation
Photodegradation and
Biodegradation
Rohella et al., 2001 used polyelectrolytes (commercially available) for removing color from pulp mill effluents. However, it remains to be seen if this method for removing color is cost effective. Because polyelectrolytes rely on ionic charge of the effluent, the color reducing ability of a method employing polyelectrolytes will be highly variable, considering the enormous fluctuations occurring in the composition of the wastewater.
The majority of color removal techniques work either by concentrating the color into a sludge or by the partial breakdown or complete breakdown of the colored molecule (Willmott et al, 1998). However, the color and chemical composition of the pulp mill effluents are usually subject to both daily process as well as seasonal variations. A single, universally applicable end-of-pipe solution has therefore not emerged to date. General physico-chemical color removal methods such as chemical precipitation, rapid sand filtration, membrane processes and adsorption have been developed (Springer, 1985). Adsorption and membrane processes, although efficient are expensive (Manjunath and Mehrotra, 1981).
Application of electrochemical methods is another way to treat wastewaters generated from cellulose paper production plants (Christoskova and Lazarov, 1988). This method guarantees high treatment efficiency but its effectiveness depends upon the types of electrodes, the construction of electrocoagulators and the conditions under which the process is run.
Chemical precipitation, using alum, ferric chloride and lime has also been studied extensively (Lathia and Joyce, 1978; Dugal et al, 1976; Joyce et al, 1979; Srivastava et al, 1984; Beulker and Jekel, 1993; Stephenson & Duff, 1996). In spite of short retention times and low capital costs, there are some drawbacks, such as the high cost of chemicals for precipitation as well as for adjusting pH, the formation of voluminous sludge due to heavy dosages of the chemicals used, problems associated with dewatering and disposing of the generated sludge as well as the high residual cation levels in the sludge, so that their color remains in the supernatant (Stephenson and Duff, 1996; Srivastava et al, 1984).
In theory, biological treatment provides an ideal solution for removing color from the effluents of pulp and paper mills. Biological treatment of the effluent produces less sludge as compared to sludge produced when a chemical treatment process is employed. Lower daily running costs are also incurred. Among the biological systems, white-rot fungi have been extensively researched upon, for their capability to degrade lignin which forms an important and major component of the pulp and paper effluents (Feijoo et al., 1995). Certain workers have shown that the pellets of white-rot fungi, under specific conditions of incubation, strongly adsorb color and AOX from the kraft bleach plant effluent (Jaspers et al., 1996).
Raghu Kumar et al., 1996, showed that marine fungi could also be utilized for removing color from bleached plant effluent. One of the strain was reported to give 74% decolorization at alkaline pH over a period of 14 days. Several other researchers have also reported partial decolorization by white-rot fungi (Eaton et al, 1980; Livernoche et al, 1983; Pronty, 1990; Gokcay and Dilek, 1994). Gokcay and Dilek (1994) have pointed out that due to the need for high glucose concentrations by the fungus, this treatment is economically non-feasible. They have also reported that the fungi were not as effective when bleaching effluents are present.
Dilek et al., 1999 have reported the decolorization of pulping effluents using a mixed culture algae. A combination of aerobic-anaerobic treatment has been used by Vidal et al. White-rot fungi excreting several extracellular oxidative enzymes including Lignin peroxidase, Manganese peroxidase and laccases were used for decolorizing bleach kraft pulp mill effluents. Up to 64% color was removed by applying aerobic-anaerobic treatment followed by enzyme treatment.
To date, there are almost no reports regarding the utilization of pure bacterial cultures for decolorization of pulping effluent. The novelty of the present invention is the application of pure cultures of bacteria, isolated from natural habitat, for removing color of the pulp and paper wastewaters in an industrially and economically viable fashion.